T-Mobile is pressing their attack; a leaked advertisement has revealed that the company will pay families up to $350 to bring their business to T-Mobile, assuming they have three or more lines.

Sound familiar? AT&T announced a similar plan last week, where they’d pay customers up to $450 to switch from T-Mobile. A far cry from their efforts to buy T-Mobile in 2011. I guess AT&T is worried that T-Mobile’s recent efforts pose a real threat to the current Big Three mobile companies - offering a range of pre-paid, no contract plans in the US has made T-Mobile a big hit - they signed around a million new customers in the last quarter of 2013 alone. Bet that’s got the rival executives a bit warm under the collar.

2013 was an aggressive year for the nation’s fourth-largest carrier; a nationwide 4G LTE network, no roaming charge for international data, and ending traditional two-year service contracts. T-Mobile’s CEO, John Legere (LEDGER) continues to make waves on social media with his resolutions to continually barrage the other major carriers.

What can I say? I like an underdog.

T-Mobile’s aggressive policies have forced the big boys to pay attention. In addition to AT&T’s switching deal, the pink T’s success induced the other carriers to offer “early upgrade” programs.

Despite these successes, rumor has it that Sprint has a $19 billion offer in the works to buy T-Mobile. Not that it makes any sense, considering how strong T-Mobile’s momentum is now. Plus they declined AT&T’s buyout in 2011, which was worth nearly $40 billion. What incentive would there be to sell a stronger version of the company for less money?

Verizon, AT&T, and Sprint are worried about T-Mobile - and understandably so. With the way 2013 went, the Big Three might just find themselves losing droves of customers - especially families. The highlight of T-Mobile’s proposed payout of early termination fees is that it would bring family plans over - it doesn’t matter than all the contract end dates on the plan would be different.

That detail always makes switching family bundles a hassle, since everyone winds up paying hefty cancellation fees. If T-Mobile changes the game, the other players will have to keep up - or lose their customers.